So far, the product data such as a variety of distribution data (date of production, eat-by freshness date, etc.) and product management data (serial number, etc.) have been printed on the industrial products in the form of line images such as bar codes and characters.
As the systems for printing the above product data, there have, generally, been known a thermal transfer system, an ink jet system and a laser system. Among them, however, the printing system based on the laser beam has now been widely employed. Namely, according to the laser system, a layer blended with a laser beam-absorbing agent and for forming laser markings is irradiated with a laser beam, and the surrounding resin is carbonized by the heat generated by the laser beam-absorbing agent to thereby form a black image. According to this system, the laser marking can be printed in the printing layer in a state where a transparent or semi-transparent protection layer is formed on the printing layer offering various advantages such as there is no need of forming a protection layer after the printing and, besides, printing can be easily done on the solid portions, too, and so on.
There have been proposed a variety of inks for use in forming the layers for printing laser markings, and a variety of laminates having a layer for printing laser markings (see patent documents 1 to 5).
Prior Art Documents:
Patent Documents
    Patent document 1: JP-A-2009-83185    Patent document 2: JP-A-03-270980    Patent document 3: JP-A-2001-113830    Patent document 4: JP-A-2008-144082    Patent document 5: Japanese Patent No. 4379668